Field of the Invention
Embodiments of the present invention relate to a chemical solution injection system and a chemical solution injection method.
Description of the Related Art
In thermal power stations and nuclear power stations, cooling water is circulated, absorbs heat generated in the power stations and comes to have a high temperature thereby. In high-temperature water, metal materials are vulnerable to corrosion. Accordingly, in plants, such as thermal power stations and nuclear power stations, where cooling water at a high temperature is circulated, it is important to secure the integrity of metal materials exposed to cooling water. For instance, it has been known that stress corrosion cracking occurs at portions of metal exposed to cooling water in nuclear power stations. Stress corrosion cracking is a phenomenon where when an alloy member subjected to a stress is placed in a corrosive environment, such as high-temperature water, cracks occur in the alloy member and the cracks rapidly develop.
Development of cracks due to stress corrosion cracking in cooling water at a high temperature can be suppressed by reducing the corrosion potential at a metal surface exposed to the cooling water. Types of measures for reducing the corrosion potential at a metal surface exposed to cooling water include measures for causing precious metal, such as platinum (Pt), or oxide, such as titanium oxide (TiO2), to deposit to the metal surface. Such a substance depositing to members exposed to cooling water is referred to as a depositing substance.
Measures for causing the depositing substance to deposit to a metal surface exposed to cooling water in a plant include measures for injecting a chemical solution containing the depositing substance into cooling water. A depositing substance component of the chemical solution injected into the cooling water deposits to metal portions in contact with the cooling water during a process of circulation of the cooling water in the plant.
Such measures are disclosed in Japanese Patent Laid-Open No. 2011-163828.
In order to provide a corrosion suppressing effect due to the depositing substance for metal surfaces exposed to cooling water in the plant, at least a prescribed amount of depositing substance is required to deposit to the metal surfaces exposed to the cooling water. Deposition of at least the prescribed amount of depositing substance to the metal surfaces exposed to the cooling water requires at least a prescribed concentration of the depositing substance contained in the cooling water.
Unfortunately, in the case of injecting a chemical solution containing the depositing substance, the chemical solution typically has a lower temperature than the cooling water has, thus causing a difference in temperature between the cooling water and the chemical solution. Accordingly, the temperature of the chemical solution injected into the cooling water sharply rises. The sharp rise in temperature accelerates deposition of the depositing substance, causing a possibility that the depositing substance deposits to some portions excessively. Such deposition excessively reduces the depositing substance concentration in the cooling water to a prescribed concentration or less, causing a possibility that the depositing substance does not sufficiently deposit to some other portions.